Inconsistency - map/collect not returning enumerator

ruby-talk
1

This seems a bit of an anomoly:

x = [1,2,3].map
x.each { |y| y*2 }

=> [1, 2, 3] # I was expecting [2, 4, 6]

It seems that Array#map and Enumerable#map without a block return just
an Array. However most other Enumerable methods return an Enumerator,
even #each (which is pretty useless, since the Enumerator maps #each to
#each)

RUBY_DESCRIPTION

=> "ruby 1.8.7 (2009-06-12 patchlevel 174) [x86_64-linux]"

[1,2,3].each

=> #<Enumerable::Enumerator:0x7fa4170ea1b0>

[1,2,3].map

=> [1, 2, 3]

[1,2,3].collect

=> [1, 2, 3]

class Foo; include Enumerable; def each; yield 1; end; end

=> nil

Foo.new.map

=> [1]

Anybody got a good explanation for this?

···

--
Posted via http://www.ruby-forum.com/\.

2

This seems a bit of an anomoly:

x = [1,2,3].map
x.each { |y| y*2 }

=> [1, 2, 3] # I was expecting [2, 4, 6]

It seems that Array#map and Enumerable#map without a block return just
an Array. However most other Enumerable methods return an Enumerator,
even #each (which is pretty useless, since the Enumerator maps #each to
#each)

RUBY_DESCRIPTION

=> "ruby 1.8.7 (2009-06-12 patchlevel 174) [x86_64-linux]"

Anybody got a good explanation for this?

Yes. You're using Ruby 1.8.7, which is, in and of itself, an anomaly :slight_smile:

But this may be to preserve compatibility with Ruby 1.8.6:

RUBY_VERSION

=> "1.8.6"

# NOT OK TO CHANGE BEHAVIOR

[1,2,3].map

=> [1, 2, 3]

# OK TO ADD BEHAVIOR

[1,2,3].select

LocalJumpError: no block given
        from (irb):3:in `select'
        from (irb):3

···

On Wed, Jan 27, 2010 at 8:29 AM, Brian Candler <b.candler@pobox.com> wrote:

3

Gregory Brown wrote:

But this may be to preserve compatibility with Ruby 1.8.6:

Ah, that's a good enough reason.

'ri Array#map' from 1.8.6 doesn't mention the possibility that it could
be used without a block, which led me off the scent.

-------------------------------------------------------------- Array#map
     array.collect {|item| block } -> an_array
     array.map {|item| block } -> an_array

···

------------------------------------------------------------------------
     Invokes _block_ once for each element of _self_. Creates a new
     array containing the values returned by the block. See also
     +Enumerable#collect+.

        a = [ "a", "b", "c", "d" ]
        a.collect {|x| x + "!" } #=> ["a!", "b!", "c!", "d!"]
        a #=> ["a", "b", "c", "d"]
--
Posted via http://www.ruby-forum.com/\.